const s1 = Symbol();
const s2 = Symbol();
const obj = {
  name: "yz",
  friend: {
    name: "hah"
  },
  // 这里不会被拷贝，弊端
  foo: function() {
    console.log("foo function");
  },
  [s1]: "abc",
  s2: s2
}
obj.inner = obj;

const info = JSON.parse(JSON.stringify(obj));
console.log(info === obj);
obj.friend.name = "heheh";
console.log(info);
